Many sensors based on porous silicon have been reported, and some use porous silicon waveguides. In particular we have previously described sensors which measure the change in refractive index of a porous waveguide: Tanya Hutter, Nikos Bamiedakis and Stephen Elliott, “Theoretical Study of Porous Silicon Waveguides and Their Applicability for Vapour Sensing”, Proceedings of the COMSOL Conference 2010 Paris, 2010; Tanya Hutter, Stephen R. Elliott and Shlomo Ruschin, Dynamic Range Enhancement and Phase-Ambiguity Elimination in Wavelength-Interrogated Interferometer Sensor, Sensors and Actuators B, 178, 593-597, 2013. Other work on porous silicon waveguides for biosensing can be found in L. Haji et al (2012). However these approaches rely on interference techniques to measure the change in refractive index of porous silicon, which limits their selectivity. By contrast, typical waveguide-based sensors provide the target material on an outer surface of the waveguide and rely on the interaction of an evanescent wave (of light propagating within the waveguide) with the analyte, which has limited sensitivity.
Other background prior art can be found in: EP0979994, EP2108944, US2012/0327398, U.S. Pat. No. 8,617,471, US2013/0081447, EP2108944, U.S. Pat. No. 8,636,955, WO2011/140156, WO2011/107868, JP2011/075513, EP2115428, US2009/059234, FR2856150, U.S. Pat. No. 6,375,725, and WO01/94915.
As noted, the above described techniques suffer from various problems including a lack of specificity and sensitivity.